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Over the next few weeks I'll explore how I'd implement support for USB audio & visual peripherals on our hypothetical string-centric CPU, & how I'd implement said peripherals. Starting with USB monitors!
For technical reasons (not wanting to boost specs beyond what's otherwise required) I wouldn't use it to extend your desktop as managed by our window manager, but rather I'd let programs do what they want with the extra monitor!
1/3?
Maybe we'd use the extra monitor to display slides to an audience? To see your aquantences in a videocall? To preview the video you're editing? To watch, or stream, others'? Or, yes, to mirror your screen?
In these cases we've got a compressed video we can stream off your harddrive or the internet over the low bandwidth (by video standards) USB2 connection to the extra monitor. The bootloader would output a brief looped video asking you to use DVI instead, for a direct GPU connection.
2/3?
The monitor would supply a description of its postprocessing pipeline, whether implemented in hardware or software, & which parameters you can tweak. Any program could tweak these, but I'd include a settings pane so you can.
The brightness setting would be automatically adjusted as a warning that the computer's about to fall asleep. Maybe a pseudo-sleep mode keeps USB alive to play the video?
Settings are configured via SETUP packets, & video via OUT packets as described by the pipeline.
3/4!
Talking about adjustments which could be made to the screen... Some operating systems (like elementary OS!) offer to shift your hue at night time to reduce the prevalence of blue light. The USB spec I'm following here provides a way for monitors to offer to do that processing! Leaving the CPU to decide when its night time & to smooth the transition.
As for the main monitor, it would incur some non-trivial overhead on our GPU. Which may encourage us to boost its clockrate.
4/4 Fin!
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